Using molecular-dynamics simulation, we study the scratching of Ti and
Mg crystals by a hard tip. Both the basal and a prismatic surface
orientations are considered. We focus on the characterization of defects
and plasticity in the crystal. Among the various types of dislocations
generated the partials b = 1/3 are most prominent.
During scratch dislocation reactions constantly reorganize the
dislocation network adherent to the scratch groove. Plastic activity is
more pronounced for the prismatic surface, where dislocation loops -
mainly consisting of b = 1/3 and 1/3 dislocations - are emitted into the substrate. Under the basal
surface I-2 intrinsic stacking faults, corresponding to b = 1/3 partials are formed parallel to the scratch groove
bottom, while they are oriented perpendicular to the surface under the
prismatic surface. We find that mainly the 01 (1) over bar0 system is activated, and relate the form of the pile-up
generated to this slip. The tangential hardness is systematically
smaller than the normal hardness under scratching. The basal surface has
smaller hardness than the prismatic surface. (C) 2015 Elsevier B.V. All
rights reserved.